The Milky Way

Dear Diary. Day Five. After an unimaginable time span of 1,800 million years after the ‘Big Bang’ stars in this area ignite forming the Milky Way, our home galaxy.

It’s somehow comforting to think we have neighbours, perhaps lots of them, in our locality. Our “town” in the Universe is called the Milky Way and as far as we know, there are between 200 and 400 million suns much like ours in town. Now 200 million stars is a big difference, but you can’t just count them.
The main problem is that our solar system is a fair way out of town, on one of the big avenues (the Orion–Cygnus arm) and there are three others just as big. (Actually we are not right on the avenue, more like a side street off one of the main avenues.)
On top of that there are all the other stars around the centre as well so scientists have to work out the approximate mass of the galaxy and divide the answer by the average size star and you get a rough idea of how many stars there are in town.
When you think that our solar system has 8 planets made up from the leftovers from the sun’s birth, it’s hard to imagine all those other suns out there don’t also have at least a handful of planets too. To add to the fun, recent data from the Kepler space mission points to planets that are not attached to stars, just wandering about, probably a couple of hundred million of them.

Getting back to planets doing the right thing, the data strongly suggest that there are up to 40,000,000,000 planets orbiting stars in the habitable zones and 11,000,000,000 of those look just like our Sun. This is just in our galaxy so all that adds up to a lot of neighbours, but don’t expect a visit tomorrow. The nearest star to us (other than the Sun obviously) would take more than four years to get to and that’s only if we can work out some way to travel at the speed of light and we don’t bump into a speck of dust or something a little larger. The closest one that might have an earth-type planet is 12 light years away.
The reason the neighbourhood has a milky look about it is that our vision has only evolved to help us find things to eat and avoid others that might want us for lunch. Our eyes did not evolve to see stars, which is why we can only see about 10,000 of them (all in the Milky Way, although some argue Omega Centauri is just outside our galaxy) meaning we can see one star in 40,000. (An exception is the temporary super-bright flash of the death of a star, a supernova). The light from the rest blends into the band of light we see on dark nights. The dark patches are caused by interstellar dust that masks the light from the stars. In the Southern hemisphere, where the dark patches are most prominent, one of the most famous is the emu, close by that Australian icon, the Southern Cross.

It must have come as quite a surprise to Galileo, to see so many stars when he put his telescope up to his Mark-1 eyeball in the year 1610. He was the guy who worked out the earth was not the centre of anything and got belted up by the Catholic Church for saying so. All the way up to the 1920’s scientists thought the Milky Way was the only show in town. Man, were they wrong, and by a margin that’s impossible to grasp. There are literally billions of other galaxies out there (170 billion to put an approximate figure on it) most of them holding between millions and billions of suns and you can’t even see one star with the naked eye, only a few distant galaxies of stars.

Our galaxy is a spiral, that is, a centre disc with 4 major arms and fairly big as galaxies go, nothing like the real big ones but not a tiddler either at 120,000 light years across. If you thought of it as a very big city 120 kilometres across, our suburb is 27 kilometres out of town on the Orion–Cygnus arm. To get our size into perspective, if our Solar System was one inch or 25mm across, the Milky Way would be about the size of China, the USA, Australia, Canada or Brazil. As we see it from Earth, orbiting the Sun and rotating every 24 hours, the Milky Way passes overhead twice a day.
In downtown Milky Way, you will find “Sagittarius A star”, a supermassive black hole, perhaps a reminder of a few cities you’ve been to. You wouldn’t want to visit this one. It’s about 4.5 million times heavier than the Sun which is about a million times bigger than the Earth. The rest of the stars rotate around this point like a big pinwheel with the arms bending back as though they were in the wind. It takes us (meaning the Sun and our solar system) about 240,000,000 years to go around once even though we do it at a cracking pace, about 220 kilometres every second so it’s a rather long way around.
What is really weird though, is one would imagine that the further out a star is from the centre, the faster it must be travelling, however that is not what scientists have found. Most stars are moving somewhere in the 210 – 240 kilometres per second range regardless of their proximity to the middle. This seems to provide evidence for unseen matter, or dark matter as it has been dubbed, that is responsible for the variation in gravity needed to make this work.
Even that seems a stately pace when you consider the Milky Way itself is belting along at 600 kilometres a second on a collision course with the neighbour galaxy Andromeda which has 3 times as many stars although scientists think the total mass is not too different.
One fleetingly pleasant thought about our Milky Way is that is has a couple of bars. Apparently about two thirds of spiral galaxies have a bar or two but as you guessed you’ll never have a refreshing nip in one of these. For obscure reasons concerning the flow of gaseous material, the central collection of stars, including the black hole have formed up into a bar shaped structure that works mightily hard as producing new stars. We make on average, one new star every year.

I guess that means in another couple of billion years, we may have new neighbours popping up on newly formed planets, but on the other hand, some stars are running out of hydrogen so there are probably lots of planets being snuffed out every year too. It’s a rough neighbourhood.


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How To Make A Galaxy

Day Four. Essentially a galaxy is a whole lot of stars clumped together, but in terms of distance, “clumped together” hardly gives an accurate impression of the size of a galaxy.

Take our own galaxy The Milky Way as an example. Our Sun is just one of somewhere between 200,000 million and 400,000 million similar stars but to get from one side of the galaxy to the other, well you’d need to pack a big lunch.
Technically, it’s possible to build a craft that could travel close to the speed of light. It would have to be very large to accommodate enough fuel to burn constantly for several years, but eventually it could reach speeds approaching 186,000 miles per second. At this speed you could get to the middle of our galaxy (once you decide where exactly that is) in about 20,000 or maybe 30,000 years. There’s probably not much chance of visiting another galaxy anytime soon.

In Universal terms however, galaxies are not that far apart and they tend to be in clusters too, anywhere from a couple of dozen to a several thousand. Virgo for example is a super-cluster and has something approaching 2,500 galaxies. Three of these galaxies are really giant ellipticals and each one is around a million light years across. Compare that against our own humble spiral’s 100,000 light years across. We’re actually in a relatively isolated group of only 50 galaxies including Andromeda, which we will get to shortly.
We shouldn’t assume that seen one galaxy you’ve seen them all. Our home galaxy is the spiral type full of extra gas and dust with long arms in which new stars are being formed continuously. Other types have practically no gas clouds and have different shapes too, including lenticular, elliptical galaxies and irregular galaxies like the dwarf Sagittarius galaxy currently being ”eaten” by the Milky Way. (It rotates through us at a right angle to the disc and every time it passes through, more stars are ripped off to become part of the Milky Way.)
Generally the galaxies with the dust forming new stars have had the least interaction or collision with other galaxies, whereas those who have been though multiple mergers tend to have “smoothed out the bumps” and mopped up most of the free gas, no longer producing new stars.
While most galaxies formed early, not so long after the Big Bang, recent data from NASA’s Galaxy Explorer telescope shows that at least some galaxies have formed in the last couple of billion years, which is not long if you are a universe.
Back when the universe was young, there were a lot of atoms of hydrogen and helium not doing much, but over time (a time scale beyond our imagination) gravity pulled them together to form clouds that by their sheer size had accumulated so much mass and gravity, became so strong, the clouds so dense, the temperature so high, we had ignition as hydrogen atoms fused under enormous pressure to start creating more helium.
These first stars tended to burn out rather quickly but gravity was still collapsing clouds and pulling the whole mass into slowly rotating disks. These attracted even more gas and dust and eventually became the size of a galaxy. Inside the rotating disc new stars formed.
Those discs of gas that were spinning slowly tended to use up all the gas making new stars and are the lens shaped galaxies we see today that no longer make stars. The faster spinning discs formed spiral arms and continue to produce stars today, in our galaxy about 1 every year.

Some of the small galaxies can have a mere 10,000,000 stars. Ten million like our Sun, which is itself a million times bigger than the earth, may seem like a lot of activity.
Imagine having a dollar for every million stars in a galaxy. If you owned a small one, you’d only have $10. If you owned the Milky Way, you’d have at least $200,000 in the bank because our home galaxy has 200 – 400 thousand, million stars.
Now if you owned a really big galaxy, you’d be rich by anyone’s standards. The larger ones have up to 10 trillion stars, which would give you 10 million dollars in the bank at just 1 dollar for every million Suns. Of course you would have to be careful how you treated the super black hole in the middle.

Ellipticals make up about 60% of the galaxies and mostly they are a lot smaller than our spiral Milky Way but a few are bigger, a lot bigger. To some extent this is a result of the number of collisions that have occurred and that has shaped and to some extent, torn apart galaxies. The few (a relative term) that are a lot bigger are the most massive galaxies in the sky. They’re a bit messy in that their stars are not lined up in an orderly fashion around a flat plane disc. No, the ellipticals have stars orbiting all over the place and mostly they are old stars and you can just about guarantee they will also have a super massive black hole at the centre. These are the ones that have the 10 trillion stars and look a bit like an egg shape or maybe a football if you don’t follow soccer (the round-ball game).

Spirals make up about 20 percent of the galaxies and generally they are the brightest so they are the most of the most visible to us. All galaxies are held together by gravity but one of the curiosities of spirals is that instead of most of the mass (and therefore gravity) being in the centre of the spiral, most mass resides in the outer edges. Spirals come in 3 main varieties and they all produce new stars on a regular basis.

The irregulars make up the rest and mostly consist of large clouds of gas and dust but have no spirals arms and have a fair mix of new and old stars. For the main, they tend to be a lot smaller than the Milky Way.
While the distances between the galaxies is quite large, when compared to the size of the galaxies, they are relatively close, certainly closer to each other in proportion than stars are to one another.
Being relatively close means a certain amount of jostling, galactic pushing and shoving. Mostly this is shadow boxing at best as the gaps between the stars is so big, they hardly ever physically collide, fist on jaw, but the gravity of the component stars twist and warp the shape of the galaxies.

Our own Milky Way is about to take on the slightly larger Andromeda galaxy which is on a collision course with us as we speak. They are so large, the gap between them is only 25 times more than their diameters. When they meet, at a leisurely 500 kilometres a second, there will be little chance of stars directly colliding, but gravity will severely distort the shape of the combined mass. After they pass through each other and throw out a few unfortunate stars into intergalactic space, they will slow down, essentially stop and start moving back towards each other again for another collision. Eventually they will become one. Of course, we will not be around to witness the best bits as the process takes somewhere between a couple of hundred million years and a really long time.

The final result of combining these two spirals will probably be an elliptical-shaped galaxy, but it could still end up an even larger spiral. We can only speculate.


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You can ignore the image. Light hadn’t been invented yet.
Perhaps the greatest understatement, serenely floating around in the nothingness (that was whatever it was before space was invented) is the term ‘Big Bang’. Nothing comes close to describing what happened in that first second, not atomic weapons, not exploding stars, not even supernovae.

If we cherish our understatements a little longer, it was hot. Not hot like anything that could be formed on a planet, not hot like the sun which by comparison is like standing next to the air conditioning on a coolish day, but really, really hot. So hot that nothing existed, not even sub-atomic particles and everything that was to come, the stars, the planets, the universe itself was packed into a space so small, by normal definition it did not even exist.
What triggered the blast may not be fully established yet, we have some competing hypotheses to work with, however it is fairly certain science will eventually create methods for testing so we can settle the matter.

What we do know is what happened in the time slot just after the ‘pop’ but like everything else on the subject, the time slot is impossibly short, far shorter than anything we mere humans can understand. (There is an hypothesis doing the rounds that quantum physicists, who do understand these things, are in fact, human too, just not ‘mere’.)
The first Planck after ignition (a Planck is like a fraction of a second but only much smaller, a billion, billionth etc.) was too hot to have nuclear forces or even gravity.(That’s 0.000,000,000,000,000,000,000,000,000,000,000,000,000,000,01th of a second if you’re interested).

As Einstein explained nothing travels faster than the speed of light, but during this briefest of periods before the second Planck (I’ll skip the zeros but there are about 32 of them) we had space inflation which did just that. Perhaps it was because there was no light yet. It was so fast, the forces blasted out were moved apart more by the expanding space than by the explosion and none of that fits with what scientists already know.
Then we had some cooling down, to temperatures that are still so hot they are way beyond our comprehension and things like gravity, nuclear forces and electromagnetism were separated into individual forces in their own right. (To be a little more accurate, the first one out of the blocks was the weak nuclear force which broke loose in the 4 zeros between the 36th and the 32nd when the inflation ended.)

Particles popped into existence by the collisions of energy particles (which have no mass or ‘weight’) into bosons which converted the energy into a particle which actually has mass. (Remember Einstein famously proved that energy and mass are the same, as is E=Mc2).
There was no ‘something from nothing’ at least from the point where the ‘bang’ occurred as there was definitely a lot of energy (another understatement) so by default there was mass as they are the same thing.
From this point on, the ‘bang’ part continued in a more prim and proper manner, ending the ‘impossible’ phase that obviously will be tested and proved eventually, but from here, the explosion was more the way we understand things behave.
The rapidly expanding universe was full of what is described as ‘a quark-gluon plasma’ which sounds unpleasant and smelly but I have on good authority, was a good thing.
When three quarks get together (facilitated by the strong nuclear force which by now had also broken into a trot) for a ménage à trois’, the result is a proton or a neutron and as you know if you throw in an electron, you end up with an atom. Quarks come in colours (who knew?) and you need three different colours to make a proton. Quarks also identify as ‘up quarks’ and ‘down quarks’ and to get the tri-colour proton, you need two ‘ups’ and one ‘down’. Electrons, by the way, are quarks that don’t go in for that sort of thing and go solo. A bit prissy by all accounts.

By the time we get to 0.000,006th of the first second, positively dawdling along, we’re got the full Monty of forces, gravity, the strong nuclear force, the weak nuclear force and electromagnetism but it is still too hot for the quarks to have their love-ins.
For this we have to wait until the first second has fully passed and the temperature a little more temperate. Now the quarks go at it like rabbits and the universe starts to fill up with protons and neutrons, anti-protons and anti-neutrons. The protons and anti-protons are more common than the neutrons and anti-neutrons but the balance of each is the same. Almost. They all get along fine until the temperature drops. By the time 10 seconds or so has passed, we’ve got our first war and the pros and the antis cancel each other out.

Well almost. For reasons yet to be explained, slightly more protons and neutrons were produced than anti-protons and anti-neutrons. After the big cancellation event, only they survived.
The surviving protons and neutrons get together in different ratios making different atoms but the temperature is so high, we have nuclear fire everywhere and some of the combinations fuse into helium. Unbelievable to non-scientists, the temperature was actually falling and by the time 17 minutes had elapsed, the fire was out.
All the neutrons were now fused into helium leaving a lot of disconsolate protons who didn’t even have an electron for company at that stage and are identified as hydrogen ions, that is, protons without an electron. To us mere mortals, the word proton and hydrogen are essentially the same thing. There are variations on the theme but isotopes devolve into complexity we don’t need to understand on the first page in our diary (or any other page for that matter).

From 20 seconds to 380,000,000 years (that’s 380 million years) may seem a bit of a jump to us with our mini time scales but for the universe it wasn’t even late morning when the hydrogen ions and the helium ions begin to capture electrons to become stable, electrically charged neutral atoms. Energy was turning into solid matter at last.
Unlike the electrons that joined the atom club, their cousins the neutrinos maintained their gypsy ways and as they have no mass, some are probably streaming through your body as we speak.
Another wanderer is the photon, particles we are more familiar with as light. They interact with the protons and neutrons but as the protons and neutrons coalesce into atoms, space becomes clear for the first time and photons of light can travel everywhere. They waste no time doing it. Quickly.

With the atoms settling into their new home and 380 million years to get their act together, they set about making babies, the first molecule.


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The First Molecule

(The DNA molecule pictured was not the first molecule)

‘Day 2’ Things were pretty quiet on a Saturday night at the Universe bar 13,800,000,000 years ago. The protons and the neutrons had been busy capturing electrons for the last 380 million years, well most of it anyway, creating all the stable atoms we were going to need to make stars and planets and zebras. But that was getting a bit monotonous.

In the open reaches of space, vast clouds of stable atoms of helium and hydrogen would later coalesce under gravity to ignite the nuclear fires that become the galaxies of stars that have come and gone in the inconceivable length of time since the beginning, but for now, some were joining forces to create organic molecules.
At least the lights were on. Space was ‘clear’ now that the electrons were under control. Photons had previously been restricted by the unattached electrons floating about but now the electrons were bound up in atoms of hydrogen and helium (mainly) the photons were free to travel. Infinitely.

The period before this, before space was ‘clear’ is called, predictably, The Dark Ages. No prizes for imagination there. The roundup and capture of the electrons by the neutrons making the space soup clear is called The Recombination and the issue of the travel permits for the photons is called Decoupling.
Stable atoms of both hydrogen and helium were all over the place, but seen one you’ve seen them all. What the universe needed was some molecules and that’s exactly what was about to happen. About 13,500,000,000 years ago, simple organic molecules were formed but before we get there we should look at the helium atoms.

Helium may be colourless, odourless and tasteless and settles for second place in abundance after hydrogen, but it has other redeeming features. It is virtually inert so it does not react with other materials and when compressed with hydrogen under sufficient gravity, it makes a wonderful star.
While the helium does not ‘burn’, it does make up about 24% of stars like our Sun (which is not due on the scene for another 8,900,000,000 years) but the fusion of the hydrogen component of the star makes more helium, eventually turning all the hydrogen into helium.
It really is a fascinating gas. Almost all the helium in the universe, despite all the new stuff being made by stars and the gas created by the degradation of uranium, was created in the first few minutes after the Big Bang.
It remains a liquid no matter how cold it gets and you need to add a considerable amount of pressure as well to make it a solid. Even so, it is difficult to tell the difference but it gets even weirder. As a liquid, helium is a superfluid which means it has no measurable viscosity. It can flow over, under or through almost anything, making it a little difficult to work with. In fact it will even crawl up the side of containers to escape. Try to imagine that.

Perversely it expands as it gets colder and it’s so crystal-clear, you need to float something like a piece of polystyrene foam on top so you can see the surface. At certain temperatures it will even leak through the solid bottom of a container.
Most space helium is the plasma version quite unlike what is found on earth. The charged particles show up here as part of the solar wind that provides us with the spectacular aurora at the poles.
Despite its abundance in space, helium, well known for its Donald Duck voice trick, is relatively rare on earth. Most of our local helium is a result of radioactive decay in minerals of uranium and thorium making about 3000 metric tons a year. In order to capture the gas, one needs to be attentive as when it is released, the earth’s gravity is not sufficient to stop it escaping into space.

It was first detected as part of the spectrum of sunlight in 1868, a few years later, an Italian named Palmieri found the first helium on earth when he was analysing the lava of Mount Vesuvius. The first significant quantities were found (in concentrations of 1 or 2%) in natural gas fields in America, still the largest supplier of the gas today.

The first primary use of helium was for air-ships, although later it became the gas of choice as a shield against oxygen in arc welding and handy for atomic bombs too. In 1927 America banned the export of what was a rare commodity and this forced the German Zeppelins to use hydrogen and we know how that turned out. By the mid 1990s, Algeria was producing enough helium to supply all Europe and is now the world’s second biggest producer.

Helium is used in purging containers, welding shielding, controlled atmospheres and leak detection but small amounts are also used in breathing mixtures for underwater work (and party balloons).
However, the main use for helium today is in cryogenics, primarily as a cooling liquid for the superconductor magnets in the medical world’s 25,000 MRI scanners. Within the MRI scanner, strong and uniform magnetic fields are produced which provoke the excited hydrogen atom protons in the water molecules of human tissue. This is what creates a signal that is processed to form an image of the body.

We’ve all heard of the largest of all molecules, DNA, but molecules come in more than a few types and sizes. At its heart though, a molecule is just two or more atoms that get together. In the case of DNA, a lot of atoms get together. While this is the standard way of defining a molecule, the exception is a branch of science called ‘the kinetic theory of gases’ where they often call any gas particle a molecule. When two atoms of hydrogen are connected, they form a homonuclear molecule, but when they are joined by an atom of oxygen we get a compound chemical called water. H2O.

Generally speaking, molecules are the basic elements of ‘soft’ matter, water, trees, animals, the atmosphere and are called organic molecules to emphasise the point.
‘Hard’ matter, rocks, metals, gems, diamonds, glass and salts are also made of atoms of course, but the atoms are chemically bonded in a different way so they have no identifiable molecules.

Molecules made of two part hydrogen to one part oxygen (water) were very plentiful and some formed in large clumps to become ice and dust comets. 380,000,000 years have passed since the Big Bang and now organic molecules are common throughout the universe and eventually, will be coming our way.


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The First Nuclear Fire. A Star is Born

Dear Diary. Day Three. Gravity has pulled massive amounts of hydrogen and helium together. The first nuclear fires, the stars, are born.

Action at last. Frankly the last 560,000,000 years since the excitement of the Big Bang have been a bit boring. Sure the protons and neutrons were rounding up the electrons and forming into nice stable atoms and the atoms were getting together making interesting things like ice, but really, something more exciting is overdue.
Before we get to that, we should get some perspective on numbers. Our world is so small and our time so short, we barely get a glimpse of big numbers unless we try counting grains of sand or something similar.

Imagine an egg carton containing 12 eggs. You know the sort, a cardboard container stacked up in your local supermarket. For this exercise, we are going to need a lot of cartons.
Begin by stacking cartons until you have a wall, 6 metres (20 foot) across and as tall as a man. Now backup and make another row the same and then just keep going, stacking up the egg cartons as high as a man and 6 metres across. If you keep going at it for long enough, you will end up a mile away (1.6 kilometres) from the first row.
But we are just beginning. We must keep stacking those cartons until we are nearly 100 miles from the beginning. Now hire a small aeroplane and climb to 10,000 feet and look down on the rows of egg cartons stretching away to the horizon in both directions. What you can see is one, yes my son just one, billion eggs.
If each of these eggs was a star, much like our Sun (which is a million times bigger than the earth) altogether they would make a smallish galaxy, a bit like the very first galaxy. It was not large as it only takes about 300 years for the light from the outside stars to reach the middle of the pack.

That galaxy could be MACS0647-JD. It’s not a very glamorous name for what may be the first galaxy, but that’s what we have called the light picked up by one of the Hubble Telescope’s programs called the Cluster Lensing and Supernova survey. The scientists had chosen a “quiet spot” to look, somewhere southwest of Orion. It is hardly sufficient to say it is long way from here because the light from this galaxy has been scooting along at 186,000 miles per second for 13,300,000,000 years and only just arrived this morning.

OK, so we accept the first one is a long way from here, but there are at least 10,000 others out there too in the same outer region and each one had their own billion stars (had, as they have almost certainly expired already).
The probing of this particular part of the universe is an extremely small window, an area equal to about one tenth of the night sky obscured by the moon. In between us and the long distant galaxy, new galaxies are still being formed so the universe is a pretty dynamic place these days.
To collect all that light from even a small part of the night sky takes time. You can’t just take a shot with your digital camera and head off to the pub. The instruments are set for lengthy periods of exposure with multiple readings collated via complex computer computations for the right result. To get the same level of detail for the whole night sky, the photography session would need to last a million years, give or take so we may have to settle for just this one spot for now.

The first fireworks display came about when massive volumes of hydrogen and helium atoms were attracted to each other by gravity, by far the weakest of the 4 forces of nature. But because the strength of gravity is governed by the mass of the objects, qualified by how close they are to each other, gravity can become somewhat pressing.
(Actually, gravity always wins because despite being the weakest force, well behind the nuclear forces and electromagnetism, it acts long-range. Eventually objects become bigger, making gravity stronger as the mass increases.)
In this case, as the atoms bumped into each other they gradually became bound together in an ever increasing mass. The strength increased with each additional atom until the new additions were pressing down on the earlier atoms with so much force, the temperature soared something approaching 15 million degrees.
When the temperature reached the critical point, the whole lot erupted in a nuclear fire that we call a star. Fortunately, the star does not explode in the normal sense or even “burn” in the normal sense as there is no appreciable oxygen to facilitate combustion.
As it happens, the temperature is so high, the pressure so great that hydrogen atoms begin to fuse creating helium and energy. Strangely, the level of energy produced by a star is fairly low when measured as a percentage of its mass, but it has a lot of mass. As a result we get a very bright spot in the sky which releases a lot of energy and in the case of the earth, that is a good thing.
Fortunately the action in the core is counter-balanced by the gravity pull on the outer two thirds, so we end up with a stable firework that will persist for about 8,000,000,000 years. Our star is about half way through and while the temperature its core is 15 million degrees, where the fusion is taking place, out on the “surface” it’s a very much milder 5800 degrees, very much less than 1% of the core temperature.

So, now we have our first stars and on the next page of our diary, we can see the formation of the galaxies.


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